Baking Textures

I have a sphere shaped as a door knob… Uv layout of front and back I exported uv layout , textured and baked… The textures are not right so i made new material and retextured the layout… With new image in UV and get the circular error on bake. What are the steps to renew the uv image material and texture for a rebake?

The circular error comes from you having the texture assigned to the mesh in the UV/Image Editor being the same as the texture that is already defined as for the object material.
And as baking is in fact baking what is in the material -> to the texture assigned in UV/Image editor, it basically bake its material texture on the texture already used by the material while trying to use that material texture as the baking reference and just can’t do that so -> circular error.

So to fix that, select your object and go to Edit Mode , select it all.
In the UV/Image Editor click on Image -> New Image to assign a new image in the UV/Image Editor to the selected mesh.

Now the baking will work without throwing any error message.
Just make sure your material are correctly defined so it really bakes what you hope to bake.